In connection with an ultrasonic diagnosis technology which, using an ultrasonic wave, allows ultrasonic images to be obtained concerning a diagnosis part in an object to be examined, the present invention relates to an ultrasonic probe which, by broadening employed frequency bandwidth, makes it possible to enhance an efficiency in the ultrasonic diagnosis, a method of manufacturing thereof, and an ultrasonic diagnostic apparatus using the ultrasonic probe.
A prior art ultrasonic probe comprised a transducer which transmits an ultrasonic wave and receives the reflected wave, a cable connected with an electrode of the transducer, and an acoustic matching layer which is fixed on the front side of the above-mentioned transducer and matches, in acoustic impedance, the transducer to a living tissue in the object such as a human body to be examined. Moreover, the above-described acoustic matching layer was formed in, for example, a one layer or two layers of seat-like form. On account of this, matching conditions for the acoustic impedance were determined so that, for a specific frequency of the ultrasonic wave generated by the transducer, the ultrasonic wave can effectively be transmitted to and received from the diagnosis part.
Concretely, matching conditions for the above-described two layers of seat-like acoustic matching layer are presented on pages 20 to 30 in "TRANSACTION ON SONICS AND ULTRASONICS" VOL. SU-13, NO. 1 (MARCH, 1966): When the central frequency of the transducer is 2.5 MHz and the acoustic impedance thereof is 28 MRayl, the first acoustic matching layer is formed with the acoustic impedance of about 8 MRayl and the film thickness which is one-quarter wavelength thick to the above-mentioned central frequency, and the second acoustic matching layer is formed with the acoustic impedance of about 2 MRayl and the film thickness which is, equally, one-quarter wavelength thick thereto.
In such a prior art ultrasonic probe, since the acoustic matching layer was formed in the one layer or two layers of seat-like form with the film thickness which is one-quarter wavelength thick to the central frequency of the transducer, matching conditions for the acoustic impedance were determined so that ultrasonic waves are effectively transmitted and received for only a specific frequency thereof. Accordingly, in the prior art ultrasonic probe, as shown in FIG. 19, the signal intensity distribution was narrower as compared with the employed frequency bandwidth. This limited a frequency bandwidth through which the ultrasonic waves are able to pass effectively and made it almost impossible for them to pass through a frequency bandwidth being off the central frequency, thus limiting frequencies available for the ultrasonic probe. Consequently, when performing diagnoses such as a pathological diagnosis of a patient with the use of one and the same ultrasonic diagnostic apparatus, the ultrasonic probe to be used therein had to be replaced depending on the following cases: Namely, for example, when observing a cross sectional image with a wide visual field, an ultrasonic probe for a low frequency had to be used, when observing a cross sectional image with a high resolution, an ultrasonic probe for a high frequency had to be used, and further when observing a bloodstream image by means of Doppler measurement, an ultrasonic probe for another frequency had to be used. This situation brought about a low efficiency in the ultrasonic diagnosis and at the same time resulted in a problem that there had to be prepared a lot of and many kinds of these ultrasonic probes.